1. Field of the Invention.
This invention relates to a solid type oxygen meter, and more particularly, to such an oxygen meter having a probe type detector adapted to produce a signal representing the difference in oxygen concentration between the inner side and the outer side of a partition wall formed by a solid electrolyte supported on the end of the probe type detector.
2. Description of the Prior Art.
FIG. 1 shows a typical known oxygen meter of direct insertion type. This oxygen meter has a probe 1 having an end adapted to be inserted into a stack or a furnace with a flange 2 thereof fastened to the furnace or stack wall 5 by means of bolts 3. The probe is provided at its end with a solid electrolyte such as zirconium, bismuth oxide or the like; detecting electrodes disposed across the solid electrolyte; temperature sensor; heater; etc. The oxygen meter further has a terminal box 4 through which the detecting electrodes, temperature sensor and heater are connected to external circuits. The oxygen meter also has a signal receiving portion 7 adapted to produce a signal corresponding to the oxygen concentration. The signal receiving portion 7 has a linearizing section for linearizing the detection signal and a temperature adjusting section employing a heater as a contro means. The oxygen meter is also provided with a pump 6 adapted to forcibly supply air as a reference gas into probe 1.
Thus, the conventional oxygen meter requires a pump for supplying probe 1 with a reference gas (air) and accordingly, the cost of production is raised uneconomically. In addition, the realiability of operation is lowered due to the employment of moving parts, such as the pump.
As an alternative, it has been proposed to adapt such an oxygen meter to introduce instrumentation air into probe 1. This system, however, requires a specific piping work and therefore, is not preferred from an economical point of view.
FIG. 2 illustrates the construction of the detecting section of the conventional oxygen meter of the kind described in FIG. 1. A probe 1' has a flange 2' adapted to be secured, for example by bolts (unnumbered) to a furnace wall or stack wall 5' with its end inserted into the furnace or stack. A test tube type solid electrolyte 8, such as zirconium, bismuth, or the like material is provided within probe 1'. Solid electrolyte 8 is secured to the end of probe 1' with its closed end located at the end of probe 1' so as to form a partition wall separating the end portion of probe 1' from other portions thereof. Electrodes 9 and 10 are closely secured to the inner and outer sides of the wall of solid electrolyte 8. A temperature sensor 11 is adapted to sense the temperature of solid electrolyte 8 which is adapted to be heated by a heater 12. Temperature sensor 11, heater 12 and a temperature adjusting section (not shown), in combination, constitute a temperature control system adapted to maintain solid electrolyte 8 at a substantially constant temperature. In operation, a signal corresponding to the difference of oxygen concentration between the inner and outer side of solid electrolyte 8 is derived from electrodes 9 and 10 through respective leads which are not shown. A filter 13 is provided at the end of probe 1' and is adapted to prevent dust from attaching to the wall surface of solid electrolyte 8. A conduit 14 has one end located at the closed end (outer side) of solid electrolyte 8 and the other end located at the portion opposite to the end of probe 1' so as to enable introduction of a calibration gas into the closed end of solid electrolyte 8.
In this type of oxygen meter, it is necessary to occasionally renew or replace the solid electrolyte 8 in order to maintain the desired precision of measurement. The amount of work required for renewal or replacement, however, is made quite troublesome and time-consuming, because probe 1' is provided with various parts at its end as described.